The invention relates to the transmission of digital data by modulation, particularly by frequency modulation, of a carrier signal.
More specifically, the invention is concerned with circuit arrangements which minimise, or at least reduce, the tendency for a frequency modulated signal in one transmission channel carrying digital data to interfere in an adjacent channel. This tendency is particularly pronounced when the frequency deviation produced by the frequency modulation is high, such as is the case where digital data is to be transmitted by frequency modulation.